1. Field of the Invention
This invention relates to a reproducing method of a high-density magnetic recording and reproducing apparatus.
2. Description of the Related Art
A typical magnetic recording and reproducing method is exemplified by Japanese Patent Publication No. 50967/1989 as re-illustrated in FIGS. 9 and 10 of the accompanying drawings.
FIG. 9 shows the manner of attachment of a magnetic head of the known magnetic recording and reproducing apparatus, and FIG. 10 is a block diagram of the known apparatus. In the known apparatus, as shown in FIG. 9, a magnetic head 1 is attached to a rotary drum 3 by a movable element 2 such as a piezo-electric element, and the magnetic head 1 is movable in the directions of arrows by inputting a signal, such as an electrical signal, to the movable element 2. As shown in FIG. 10, the known apparatus includes a detector 8 for detecting the output of the magnetic head 1, a stepped signal generator 12 for generating a stepped signal, an analog/digital converter 18 for converting the output signals from the detector 8 and the signal generator 12 into digital signals, a memory 9 for storing the output of the analog/digital converter 18, an arithmetic operating unit 10 for performing a predetermined arithmetic operation on the content of the memory 9, and a digital/analog converter 11 for converting the result of the predetermined arithmetic operation into analog signals. The known apparatus also includes a sampling signal generator 15, amplifiers 14 and a reproducing mode changeover generator 13 for operating switches SW1, SW2.
To start reproducing, the reproducing mode changeover generator 13 is first operated to activate the switches SW1, SW2 as indicated by the dotted lines. A several-step signal (three-step signal in this example) generated from the stepped signal generator 12 in terms of fields as shown in FIG. 11 is applied to the movable element 2. Since the movable element 2 moves the magnetic head 1 transversely to the track 5 according to an applied voltage, the magnetic head 1 scans the positions a, b, c of FIG. 12 relative to the track 5. When making one scanning of the track 5 (about 17 ms), the magnetic head 1 does not change the applied voltage. At that time the reproduction output from the magnetic head 1 shows characteristic waveforms 16, 17, 19, depending on the position of the magnetic head 1. Also, at that time, the stepped signal voltages and the output waveforms 16, 17, 19 are stored in the memory 9 in a predetermined sampling period, and the switches SW1, SW2 are turned off. (See the position b of FIG. 11).
Given that the output waveforms 16, 17, 19 correspond to the applied voltage from the stepped signal generator 12, it is possible to obtain an amount of curvature of the track 5, for example, as shown in FIG. 14. In FIG. 14, with the optimum track position such that the reproduction output waveforms 16, 17, 19 from the magnetic head 1 are maximized, the waveform 20 connecting the successive points smoothly is produced by the arithmetic operating unit 10, and then the curvature of the track 5 is calculated. For increasing the degree of precision of tracing the track 5 by the magnetic head 1, if it is understood how high the reproduction voltage Vd at a maximum is outputted by the magnetic head 1, an amount of displacement of the track 5 is calculated from the difference between its voltage value (design voltage value) Vd and the maximum value when reproducing, and this difference must be canceled. Now assume that a maximum value is V.sub.max ; if it satisfies the following equation: EQU .vertline.V.sub.d -V.sub.max .vertline..ltoreq..epsilon.
where .epsilon. is a very small value, and the magnetic head 1 can be regarded as substantially tracing the tracks exactly.
The obtained amount of curvature of the tracks is stored again in the memory 9. With the switches SW1, SW2 being turned off, a voltage for compensating the amount of curvature of the track 5 is applied from the point b of FIG. 11 to the movable element 2 via the digital/analog converter 11 at each scanning by the magnetic head 1 so that the best tracking can be performed without normally vibrating the magnetic head 1.
Only at an instantaneous time (the distance between the points c and d in FIG. 11) when the tape running mode is changed, is a stepped signal generated whereupon a new compensating signal is created in the previously described procedure.
In the case of a VTR, since the time needed for each scanning of the magnetic head 1 is about 17 ms, the period to generate stepped signals for ten scanning is about 170 ms, which has no adverse effect on the quality of picture.
In the foregoing example, the amount of curvature of the track 5 is obtained only while stepped signals are generated. Alternatively, in the beginning period of the duration between the points b and c in the application of the memory voltage of FIG. 11, the output voltage of the magnetic head 1, which is obtained by compensating the curvature of the track 5, may be compared with the design voltage value Vd, and checking may be made on whether the voltage for compensating the curvature of the track 5 is adequately high. If the voltage is inadequately high, the stepped voltage may be superposed with the track curvature compensating voltage to calculate the amount of track curvature again in an effort to improve the degree of compensating precision.
According to this known method, regarding even a magnetic tape on which information is recorded by the same magnetic recording apparatus, the curvature of the track 5 is subjected to changing with time such as due to the extending and shrinking of the magnetic tape as well as the changing of tension of a reproducing apparatus. Consequently, some measures are needed to meet with this changing with time.
In the known method, as described also in Japanese Patent Publication No. 50967/1989, the quality of the picture is deteriorated during the period immediately after reading of signals is started, namely, while stepped signals are generated. To follow the track curvature change with time, it is necessary to provide a period where stepped signals are generated during reproducing, which deteriorates the quality of the picture at the generation of each stepped signal. Further, for example, in the case of an ordinary home magnetic recording and reproducing apparatus, a magnetic tape to be reproduced can be recorded by a variety of magnetic recording apparatuses. Since there are individual differences in record levels between these various apparatuses, it is impossible to define the design voltage value uniquely so that the degree of precision of compensating the track curvature cannot be improved by a comparison with a constant value Vd.